A cellular radio access network is a collection of cells that each includes at least one base station capable of transmitting and relaying signals to subscribers' wireless devices. A “cell” generally denotes a distinct area of a mobile network that utilizes a particular frequency or range of frequencies for transmission of data. A typical base station is a tower, to which a number of antennas are affixed, and the antennas transmit and receive the data over the particular frequency. Wireless devices, such as cellular or mobile phones, smart phones, camera phones, personal digital assistants (PDAs) and laptop computers, may initiate or otherwise transmit a signal at the particular frequency to the base station to initiate a call or data session and begin transmitting data.
Mobile service provider networks convert cellular signals, e.g., Time Division Multiple Access (TDMA) signals, Orthogonal Frequency-Division Multiplexing (OFDM) signals or Code Division Multiple Access (CDMA) signals, received at a base station from wireless devices into Internet protocol (IP) packets for transmission within packet-based networks. A number of standards have been proposed to facilitate this conversion and transmission of cellular signals to IP packets, such as a general packet radio service (GPRS) standardized by the Global System for Mobile Communications (GSM) Association, a Universal Mobile Telecommunications System (UMTS) architecture, an enhancement of UMTS referred to as Long Term Evolution (LTE), mobile IP standardized by the Internet Engineering Task Force (IETF), as well as other standards proposed by the 3rd Generation Partnership Project (3GPP), 3rd Generation Partnership Project 2 (3GPP/2) and the Worldwide Interoperability for Microwave Access (WiMAX) forum.
A typical 3GPP mobile service provider network, or mobile network, includes a core packet-switched network, a transport network, and one or more radio access networks. The core packet-switched network for the mobile network uses a variety of control protocols to authenticate users and establish logical connections, known as bearers, among the many service nodes on a path between a wireless device, attached to one of the radio access networks, and a packet data network (PDN). The service nodes then utilize the bearers, which employ data protocols, to transport subscriber traffic exchanged between the wireless device and the PDN, which may include, for example, the Internet, an enterprise intranet, a layer 3 VPN, and a service provider's private network. Various PDNs provide a variety of packet-based services to wireless devices to enable the wireless devices to exchange service data with application or other servers of the PDNs.
Various network devices are positioned between mobile devices and PDNs. For example, serving gateways (SGWs), PDN gateways (PGWs), or other intermediate devices (such as service devices of a service network) may be positioned between a mobile device and the PDN. In general, such network devices may be referred to as intermediate network devices. Intermediate network devices may also be present in networks other than mobile networks, e.g., conventional computer networks. For example, routers, switches, service devices, gateway devices, firewalls, intrusion detection and prevention devices, and the like are examples of intermediate network devices that need not necessarily be used in a mobile network context.
In some cases, intermediate network devices may be configured to act as transmission control protocol (TCP) proxies. That is, the intermediate network devices may acknowledge received packets to a device from which the packets were received (e.g., a client device) and then forward the received packets to the intended destination (e.g., a server device). This process is performed transparently to the endpoints of the devices. Acting as a TCP proxy allows the intermediate network device to perform certain services, such as security services. For example, by acting as a TCP proxy, the intermediate network device may perform deep-packet inspection to extract deep application-level information and exercise appropriate control, such as charging different applications differently, maintaining analytics of data sessions, or drop sessions or applications that a user is not subscribed to.
When an intermediate network device acting as a TCP proxy becomes inactive (e.g., fails or is intentionally brought down for maintenance), many TCP network sessions may be brought down altogether, and if the TCP state is not synchronized, these connections are lost. The client device then needs to open new connections to restart a corresponding network transaction. This may result in a new intermediate network device receiving data of a previously ongoing session. During a failover state, a conventional intermediate network device generally either allows traffic to pass through unproxied, or drops the traffic. In other cases, backup network devices have been configured to receive large amounts of synchronization data from primary network devices.